1. Field of the Invention
The present invention relates to digital switching systems and more particularly to a pulse monitor circuit for use in such systems.
2. Description of the Prior Art
Typical digital pulse monitor circuits require complex logic circuitry and often are unreliable and subject to race conditions. A recent advancement in the state of the art was disclosed by H. Ballentine in an article entitled "Clock-Activity Detector Uses One DIP", Electronic Design News, Jan. 5, 1980, page 156. However this circuit is subject to the following problems; potential race conditions for some circuit implementations due to insufficient clear pulse widths; any detected failure signal is cleared when the monitored pulse signal reappears; and it is unable to detect reference signal failures.
Accordingly it is the object of the present invention to provide a minimum component, highly reliable pulse monitor circuit, free of any potential race problems, resettable by either an external clear signal or reappearance of the monitored pulse, and capable of detecting failures of both the monitored and reference pulse signals.